Over-pressure protective device



June 26, 1951 A. P. B`ENTLEY OVER-PRESSURE PROTECTIVE DEVICE Filed June19, 1950 a 7? 7 Z c 4 M a m i mnu uw ,mnu/QZ.. rv nm \\Vf f b i /w M n au 0 a L ///J/////// :4J 0 .J r4 :4 4 f ly .M w3. L u.) 4 4.. 'n

. Invehor: Arthur E? Bentley His Attorney.

Patented June 26, 1951 2,558,534 OVER-PRESSURE PRTECTIVE DEVICE ArthurP. Bentley, Scotia, N. Y.,

assignor to General Electric Company, a corporation of New YorkApplication June 19, 1950, Serial No. 169,020

(Cl. 'I3-389) 3 Claims.

This invention relates to 'an over-pressure protective device and, inparticular, to a protective device for a diierential gauge of the typeused to measure the flow of an expansible fluid through a conduit.

By conduit is meant any conductor which is adapted to constrain acompressible uid and direct its flow. The flow may be caused by apressure differential produced by the resistance of a heat exchanger, anorifice in an obstruction plate, or the like. The pressure differentialproduced by such a resistance can be correlated with the rate of flowthrough the conduit; consequently, it is important to be able to measurethe pressure differential.

A differential pressure gauge is a convenient apparatus for making suchmeasurement. By differential gauge is meant an instrument responsive todierence in pressures on opposite sides of a resistance. The pressuredifferential is indicative of the flow across that resistance and, inaddition, the pressure differential indicates the value ofthe resistanceoffered. This pressure differential can be transmitted to a meter for adirect reading of the differential pressure.

In diierential gauges of the type described, frequently one of theoperative elements is a delicate bellows4 that expands and contracts inresponse to the pressure dierential on its opposite sides. Because ofits delicate sensitivity, however, a high unbalanced pressure willrupture the material of the bellows. Such a high unbalanced pressure canbe a result of the explosion that takes place within the expansibleiluid or it can be caused by an obstruction that blocks the passage offluid through the conduit.

It should be pointed out at this time that while a bellows operateddifferential meter has been and will be referred to, such a referencehas been selected merely to illustrate more clarly the operation of.this invention, and it is not intended to .be a limitation of its scope,which-is broad enough to operate on many types of differential meters. I

It is an object of this invention to provide a device which will protecta differential meter against an excessive differential pressure.

It is a further object of thisinvention to provide a new and improvedover-pressure protective device for a differential gauge.-

It is a still further object of this invention to provide a new andimproved over-pressure protective device that operates in response tocompressible uids to automatically disengage a differential gauge from apressure source to be measured.

It is a stil further object of this invention to provide a new andimproved over-pressure protective device that is simple in constructionand automatic in operation.

Further objects and advantages of this invention will become apparentand the invention will be more clearly understood from the followingdescription referring to the accompanying drawing, and the features ofnoveltywhich characterize this invention will be pointed out withparticularity in the claims annexed to and forming a part of thisspecification.

Briefly, this invention comprises a device responsive to a predetermined'pressure diffential between two points or on opposite sides of someobstruction or resistance within a conduit to activate valves that cuton the supply of compressible fluid to a differential gauge whereby thegauge is temporarily isolated from the conduit; the compressible fluidwithin the dierential gauge is balanced to equalize the pressure actingon the differential gauge; and finally when the differential pressure inthe conduit again recedes below the predetermined limit, the gauge isautomatically reconnected to the conduit.

In the drawing, the single figure is a simple schematic drawing of theoperating elements of this invention.

Referring to the drawing, a conduit l is shown having an obstruction 2defining a central orifice or opening 3. The obstruction 2 separates theconduit into a compartment 5 which is the high pressure compartment anda compartment 5a which is the low pressure compartment. The differencein pressure between the two compartments is caused by the resistance tothe flow of compressible uid o`ered by orice 3.

An over-pressure protective device 6 comprises a pair of axiallyjuxtapositioned cylinder blocks i and 1a which are spaced apart by aflexible diaphragm 8 and removably interconnected by a plurality ofbolts 9.

.Cylinder blocks 'l and 'la each provide a cylinder l0 and il,respectively, which, in turn, are separated by the flexible diaphragm 8.

As will be hereinaftery described, cylinder I0 is further subdividedinto three cylindrical compartments Illa, Illb, and Illc, while cylinderIl is subdivided into three cylindrical compartments Ila. IIb, and llc.

TheI cylindrical compartment ib is provided with a piston I3 which isaxially slidable therein,

, 3 and cylindrical compartment a second piston I4 which is axiallyslidable therein. The two pistons, in turn, are rigidly-interconnectedby an axial rod I5 which causes the pistons to move one with the other.

Diaphragm 8, which divides cylinder blocks 1 and 1a, is generallycircular and provided with an axial opening through which rod I5 ispassed. Diaphragm 8, which in a preferred embodiment is made of neopreneor other impregnated material, is secured to rod I5 substantially midwayalong its length, either by cement, or by a ring (not shown).

Piston I3 is provided with a threaded bore I8 and a threaded ferrule I1that is provided with a central axial passageway I8, while piston I4 isprovided with a threaded bore I9 and a threaded ferrule 20 that isprovided with a central axial passageway 2l. In accordance with thisstructure, piston I3 divides cylinder I0 into compartments IIlb and IIlcwhich are interconnected by passageway I8, while piston I4 dividescylinder II into compartments IIb and IIc which are interconnected bypassageway 2 I.

In order to guide the axial movement of rod I5, a web 22 is provided incylinder block 1 and a web 23 is provided in lower cylinder block 1a.Web 22 separates compartment IIIb from compartment Illa, while web 23separates compartment IIb from compartment IIa. Web 22 is provided witha passageway 24 that provides communication between compartment IIIa andcompartment IUb, while web 23 is provided with a passageway 25 thatprovides communication between compartment IIa and compartment IIb.

With this structure, the steady state pressure in compartment Illa isalways equal to that of compartment Illb, while the steady statepressure in compartment IIa is always equal to that of compartment I Ib.Furthermore, in a steady state condition, the pressure in compartment Icis equal to that of compartments I0b and Illa, and the pressure incompartment IIa is equal to that in compartments I Ic and 'I Ib, sincethe compartments on each side of diaphragm 8 are all interconnected.

A meter 26 is shown as comprising a cylindrical shell or housing 21dening a, compartment 28, which is subdivided by an expansible bellows30 to provide a compartment 29. The diierence in pressure betweencompartment 28 and compartment 29 causes bellows 30 to expand orcontract, depending upon the direction of the pressure differential. Arod 3I is connected to and supported by the free end of bellows 30. Rod3| extends through the upper portion 32 of Icylindrical housing 21 andis supported by a packing nut 33. Rod 3| is pivotally connected to ameter needle 34 which pivots about a fulcrum 35,. A point 36 on needle34 indicates on a scale 31 the -pressure diierential 4betweencompartments 29 and 28 in response to the movement of bellows 30.

A conduit 38 connects the high pressure side of conduit I toover-pressure device 8. A bore 39 through cylinder block 1a registerswith a bore 40 through the skirt of piston I4 to allow the compressibleilud to pass from the high pressure side 5 of conduit I to compartment IIc on the bottom of piston I4. A bore 4I in cylinder block 1a connectscompartment IIb above piston I4 with conduit 42 that connects theover-pressure device 8 with the housing 21 of meter 25. Conduit 42conducts the compressible fluid from compartment IIb to compartment 29within the bellows 30.

I Ibis provided withv duit 41 allows the compressible fluid fromcompartment IIIc to pass into the meter compartment 28 and act inopposition to the pressure within compartment 28.

A cap 48 threadedly engages the internal threaded end 48a of shell 1 anda plug 43 threadedly engages a threaded recess 48a in the upper end ofcap 48. Plug 49 and cap 48 define a valve chamber 50.

A valve 5I is positioned in valve chamber 50 and has a valve stem 52that passes through cap 48 into compartment Illc. Valve stem 52 ispositioned to be actuated by piston I3 to be raised to expose a bore 53provided in cap 48 that interconnects valve 5II with bore 46. Cap 48 isfurther provided with an opening 54 `that threadedly engages a conduit55 that interconnects conduit 42 and valve chamber 50.

With this structure, when valve 5I is raised by piston I3, thecompressible fluid in conduit 42 can pass through conduit 55 into valvechamber 50, thence past valve 5I into bore 53 to bore 48 and conduit 41to balance the pressure in conduits 42 and 41. A spring 55 isinterpositioned between plug 45 and valve 52 to maintain it closed overbore 53. Spring 56 is a light spring that serves the sole purpose ofkeeping the valve closed. A second spring 51 is calibrated and definesthe operating differential at which the over-pressure device willfunction. Spring 51 is positioned between cap 48 and piston I3 toprevent piston I3 from opening valve 52 until the force exerted byspring 51 is offset by pressure on pistons I3 or I4 after an explosionor by diaphragm 8 if a high differential is slowly built up. The pistonsI3 or I4 do not actuate the valve when the high differential is slowlybuilt up because of the interconnecting passageways heretoforedescribed.

Since cap 48 is threadedly engaged with shell 1, the spring 51 isreadily removable to be interchanged with one having a different springconstant. This structure permits the differential rating of theover-pressure protective device to be changed. y

In operation, this new and improved overpressure device operates andfunctions as follows. Expansible fluid, such as gas, air, or the like,from the high pressure side 5 of conduit I passes through conduit 38 andbores 39. and 48 to compartment IIc to act on the bottom surface ofpiston I4. The expansible fluid from the low pressure portion 5a ofconduit I' passes through conduit 43 and and bores 44 and 45 tocompartment IIIb to act on the lower surface of a piston I3. Theexpansible fluid from-compartment IIc passes through bore 2| in ferrule25 to the upper surface of piston I4 into compartment IIb and throughbore 25 to compartment IIa to act on one side of diaphragm I2. 'I'heexpansible uid from compartment IIIb passes through bore 24 tocompartment Ilia to act on the other side of diaphragm I2. Under theseconditions, the pressure from the low side 5a of conduit I, plus thepressure of the interchangeable spring 51, acts in one vdirection on rodI5 and diaphragm 8, while the expansible fluid from the high pressurecompartment in conduit I acts in the other direction on rod I5 anddiaphragm 8. Under normal operating conditions for any selected spring51, a steady state condition exists and a continuous supply ofexpansible fluid acts on either side of the bellows 30 in meter 26. Thepressure balance between compartments 28 and 29 on either side of thebellows influences the direction of needle 34 and its reading on scale31.

If an explosion occurs, for example, in the high pressure compartment 5of conduit I, then high pressure fluid passes through conduit 38 to thelower surface of piston I4 to force piston I4 and rod I5 up; thus,piston I4 closes over bore 4I and piston I3 closes over bore 46. Thisshuts of the supply of expansible fluid to meter 26 and, thus, protectsit from the high differential pressure that might exist because of theexplosion in-the high pressure compartment. In addition, as rod I5 andpistons I4 and I3 are moved up, valve stem 52 is actuated to raise valve5I and interconnect conduits 41 and 55. With the passage of fluid fromthe high pressure conduits 42 and 55 into valve chamber 50 and throughit into conduit 41, the pressure in compartments 28 and 29 of meter 26is equalized to relieve any strain on bellows 30.

As soon as enough of the compressible fluid passes through orifice 3 inconduit I to reduce the high unbalanced pressure between compartments 5and 5a in conduit I, the pressure from compartment 5a of conduit Iacting on one side of diaphragm 8, plus the pressure caused by spring51, will offset the .pressure from the high pressure compartment 5acting on the opposite'side of diaphragm 8, whereupon piston I3 andpiston I4 connected by rod I5 will move down to expose bores 44 and 4I,respectively. This movement connects meter 26 to conduit I and thedifferential pressure is again recorded. With this structure, it isobvious that the over-pressure protective device is an automaticinstrument that responds to any differential pressure beyond the presetdifferential determined by spring 51. Specically, if the differentialpressure de- -III termined by spring 51 is exceeded, the over-pressureprotective device automatically disconnects meter 26 from conduit I;then, when the differential again recedes below the predetermined limit,the over-pressure device automatically reconnects meter 26 to conduit I.

It is to be noted that whether the high pressure differential is causedby either an explosion or whether the high differential is slowly builtup, the over-pressure protective device still functions to shut off thesupply of the expansible fluid to the meter. Obviously, the use of suchan over-pressure protective device saves much time and effort andexpense, since it protects sensitive differential instruments from highunbalanced pressures` Modifications of this invention will occur tothose skilled in the art and it is desired to be understood, therefore,that this invention is not to be limited to the particular embodimentdisclosed, but is intended to cover all modifications which are withinthe spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An over-pressure protective device for automatically disconnecting apressure gauge from a source of differential pressure at a predeterminedvalue of differential pressure comprising a cylinder block having twoaxially aligned cylinders, a flexible diaphragm separating saidcylinders, a separate piston movably mounted in each ot' said cylinders,a rod rigidly interconnecting said pistons secured to said diaphragm,conduit means connecting corresponding sides of said pistons one to eachside of said press-ure differential source, conduit means connectingsaid cylinders to the pressure gauge, said pistons moving in response toa predetermined pressure differential to close said conduit meansconnecting said cylinders to the gauge.

2. An over-pressure protective device for automatically disconnecting adifferential gauge from a differential pressure source at apredetermined value of differential pressure and for automaticallyre-connecting the differential gauge to the source when the differentialpressure decreases to a value less than said predetermined value,comprising a circumferential wall defining an axially extending cylinderto house a first piston and a second piston, each slidable in saidcylinder, a rod rigidly interconnecting said pistons, a

-flexible diaphragm secured to said rod transverse to the axis of saidcontinuous wall to divide said cylinder into two axially juxtapositionedcompartments, conduit means for conducting an elastic fluid from thehigh pressure side of said differential source to one side of said rstpiston, conduit means for conducting an elastic fluid from the lowpressure side of said difertial source to the corresponding side of saidsecond piston, each of said pistons having a steady state position andan actuated position, conduit means positioned in said wall above thesteady state position of each of said pistons to connect saidover-pressure device to said differential gauge, said pistons beingactuated in response to a sudden predetermined pressure differential toclose said conduit means positioned above said piston steady stateposition to prevent rupturing of said differential gauge.

3. An over-pressure protective device for automatically disconnecting adifferential gauge from a differential pressuresource at a predetermined'value of differential pressure and for automatically re-connecting thedifferential gauge to the source when the differential pressuredecreases to a value less than said predetermined value, comprising ahollow cylinder block defining a central cylinder, a first piston and asecond piston each slidable in said cylinder and each having an actuatedand a steady state position, a rod rigidly interconnecting said pistons,a flexible diaphragm secured to said rod transverse to the axis of saidcylinder to separate said cylinder into two axially juxtapositionedcompartments, a hollow cap positioned at the end of one of saidcompartments, a valve including a valve rod positioned in said cap withsaid valve rod extending therethrough into one of said axialcompartments to be actuated by the movement of the first of saidpistons, a plug in said cap at the end opposite said valve to definewith said cap a valve chamber, a first spring positioned between saidvalve and said plug to maintain said spring in a closed position, acalibrated spring positioned between the end of said cap and the firstof said pistons to surround said valve rod, conduit means for conductingelastic fluid from the high pressure side of said differential source toone side of the second of said pistons, a bore extending through saidsecconducting an elastic iluid from the low pressure sideof saiddiiierential source to a corresponding side of said iirst piston'and tothe other side of said diaphragm, conduit means positioned' above thesteady state position of each of said pistons to connect saidover-pressure devices to said diierential gauge, conduit meansconnecting said conduit positioned above said steady state position ofsaid second piston to said valve housing, said pistons automaticallyresponding to a sudden predetermined pressure dinerential to close saidconduits positioned above said piston steady state positions to isolatesaid diierential gauge from said differential pressure source and toactuate said valve rod to interconnect said conduits connecting saiddifferential gauge to said over-pressure protective device to balancethe pressure in said conduits and to relieve any stress on saiddifferential gauge, said diaphragm automatically responding to a slowlys a l v built-up predetermined differential te pressnnvmovesaicipistonstcitlieiractuatedlpositiamtoA close said conduitspositioned above said piston steady state position to isolate saiddiilerentisl. gauge from said'dierentialpreesure source, said pistonsautomatically returning -rw theirsteady state position when saiddierential pressure recedes below said predetermined level toautomatically re-connect said diiiereniial gauze to said diiierentialpressure source.'

ARTHUR P. my.' summons crrsn The renewing references are of ille of thispatent: record m the UNITED STATE PATENTS

